This invention relates to an apparatus for determining road shape.
Conventional navigation apparatus in a vehicle such as a car uses a position detecting unit such as GPS (Global Positioning System) or various kinds of sensors to detect a current position of the vehicle. The navigation apparatus searches and displays a route from the current position to a destination point for use by a driver of the vehicle.
Often vehicles in which the navigation apparatus is installed include a power train control apparatus for controlling the vehicle driving force based upon road status data provided by the navigation apparatus. For example, if navigation data indicates that the vehicle is entering a corner (curve) and that vehicle operating conditions exceed preset conditions, the power control executes a corner control procedure such as slowing the vehicle and possibly shifting down to a lower shift gear level from a higher gear level. During a down shift the power control operates the transmission to change a small transmission ratio to a larger transmission ratio.
In determining the need for controlling the vehicle driving force, the control apparatus executes a calculation procedure based on various kinds of data such as road status data, vehicle speed, accelerator opening and the like which are provided from the navigation system. Based upon these calculations, control data are created to control the vehicle for various corresponding detected road status conditions (refer to, for example, Japanese Unexamined Patent Application Publication No. 2001-93094).
A database of stored map data in the navigation apparatus contains node point data which indicate positions and shapes of roads. The density or closeness of successive node points is used to determine the radius of curvature of a road, i.e., curves with a small radius of curvature are indicated by closely spaced node points (high density) while curves of larger radius are indicated by more distantly spaced node points (low density). However, often the node points at sharp bends or corners of roads, such as at corner entrances, are set at a low density so that the shape of a curve determined by density of node points may be different from an actual road shape.
Where node points such as in corner entrances are set only in low density, the curvature and the start and end points of the corner can not be determined based upon the density of the node points. Thus, it is not possible to execute an appropriate corner control at such corners.